1. Field of the Invention
The present invention relates to a developing solution (a developer) for producing printed circuit boards and a process for producing printed circuit boards. More particularly, the present invention relates to a developing solution for producing printed circuit boards which comprises a quaternary ammonium hydroxide or a quaternary ammonium hydroxide and a quaternary ammonium hydrogen carbonate, and a process for producing printed circuit boards comprising adhering a resist of the photo-curing type on a board, exposing the resist to ultraviolet light through a photomask, developing an exposed resist by using the alkaline developing solution and forming a plating resist circuit or an etching resist circuit.
2. Description of the Related Arts
Circuit processing of printed circuit boards in recent years has become finer in parallel with the progress of surface mounting of mounted parts. Even so called circuits of five lines between pins in which five signal lines are placed between through-holes on the base grid have been designed.
In this case, it is required in the design that the signal width and the distance are both 0.08 mm. A process for producing such fine circuits with stability has been desired.
As the plating resist and the etching resist, photo-resists of the photo-curing type having a thin-film structure have been recently developed for the purpose of forming fine circuits and attracting attention. Adhesion of a photo-resist by the electro-deposition method is also attracting attention. Photo-resists of the dry film-type have been improved in recent years so that they can be applied to forming fine circuit boards.
For all these types of photo-resist, an aqueous solution of sodium carbonate is generally used as the developing solution in the development process.
In the development of a photo-resist, saponification between the resist and an alkali proceeds as the photo-resist is dissolved into the developing solution and foaming of the developing solution is increased to cause trouble in the developing apparatus. Therefore, it is the real situation at present that a defoaming agent containing an oil component such as silicone oil as the main component thereof is added to suppress the foaming of the developing solution.
However, such additives (defoaming agents) are expensive. Furthermore, insoluble substances are formed in the developing solution when such defoaming agents are used and big problems arise for forming a circuit, particularly in the case of the plating resist and the etching resist.
When a developing solution containing sodium carbonate is used, a washing treatment with water is conducted for removing water containing alkaline substances which remains on the printed circuit board after the development with sodium carbonate is finished. However, the removal of the alkaline substances is very difficult. The developing apparatuses currently used are generally equipped with washing tanks in five stages or more for completely removing the insoluble substances.